1. Field of the Invention
The present invention relates to an improved mutant vaccinia virus and a process for the production thereof.
2. Description of the Related Art
The vaccinia virus was originally developed as a vaccination virus. Recently, however, vaccinia virus has drawn attention as a vector for a recombinant technique, a gene coding for an antigenic protein of a particular pathogenic virus, i.e., exogenous antigen gene, is introduced into a vaccinia virus gene as a vector for the construction of a recombinant vaccinia virus. According to this technique, the development of a vaccine against viral disease, which has been difficult so far, can be realized. Therefore, the vaccinia virus has become useful as a vector virus for the construction of a recombinant vaccinia virus.
A virus for a vaccine must have both a high proliferation potency and a low toxicity (pathogenic potency?), especially neurovirulence. Therefore, to obtain a recombinant vaccina virus by introducing an exogenous antigen gene into a vector vaccinia virus, the vector vaccinia virus per se. must have the above-mentioned desired properties.
The Lister original (LO) strain of the vaccination virus has a high proliferation potency, but at the same time a ralatively high neurovirulence, which is disadvantageous as the vaccination virus and as the vector for the construction of a recombinant virus as a vaccine. As an improved vaccination virus which does not have this disadvantage, a mutant Lister clone 16 (LC16) has been from the Lister original (LO) strain (Hashisum et al. Vacinia Viruses as Vectors for Vaccine Antigens, Elsevier, 1985, p 87-99).
The above-mentioned LC16 was passaged six times on RK cells and cloned by a plaque method to obtain a mutant LC16m0 strain which provides relatively small and even-size pocks on a chorio-allantoic membrane. The mutant LC16m0 was further passaged three times and recloned to isolate an LC16m8 strain, which exhibits a very small pock size. The LC16m8 is advantageous as a vaccination virus in that it has a low neurovirulence, a low proliferation potency in the brian, a low invasion potency, a low recovery of virus from virus inoculated brain, and provides a good histopathlogical feature of the brain after inoculation of virus. However, the LC16m8 is disadvantageous in that it has a low proliferation potency in the skin and a low in vitro proliferation on Vero cells (Hashizume, Rinsho To Virus, Vol 3, No. 3,225-235, 1975).
The gene structures of the original LO strain and the mutant LC16m8 strain were compared, and it was found that a Hind III D fragment of about 10 kb derived from the LC16m8 carries an Xho I site, although a corresponding fragment derived from the LO does not carries the Hind III site, suggesting that genes related to the proliferation and neurotoxicity of virus are present on the Hind III D fragment (Sugimoto et al., Microbiol. Immunol. Vol 29 (5), 401-428, 1985).
As seen from above, although a vaccinia virus which has a high proliferation potency and high pathogenic properties, and a vaccinia virus which has a low proliferation potency and low pathogenic properties, including neurotoxicity, are known, a vaccinia virus possessing a high proliferation potency with a low pathogenic properties is not known.